Switchgrass and River Oats
In Autumn grasses take a more prominent place in the garden. In our garden, there are two grasses that do really well: Sea Oats (Chasmanthium latifolium) and Switchgrass (Panicum virgatum). There are also sedges (Carex sp.) that do well, but that’s a different story.
In my opinion River Oats have the most dramatic seedheads of all the ornamental grasses, especially when backlit by the sun. Another good thing about River Oats is that it will grow in sun or shade.
The downside of this grass is that it pops up all over the place, and the seedlings are tenacious little buggers. I try to cut down about half the seeds before they shatter, but even so I am pulling up trespassing River Oats all through the summer. Despite the nuisance factor, I’m not tempted to dig up our River Oats, because they just look really good.
River Oats are also called Northern Sea Oats, which is a mystery because they don’t grow by the sea. They do grow near woodland streams, though they’ll grow in our garden without needing a lot of moisture. The seedheads bear a slight resemblance to real oats, but the two plants are not in the same genus.
Switchgrass has a very different character. The panicles of tiny flowers have an ethereal, cloud-like quality. While River Oats have an arching habit, the stems and leaves of Switchgrass tend to be stiffly upright. It’s a big grass, about 6 feet tall (2 to 3 feet taller than River Oats), and is prominent in tall-grass prairies.
The roots of Switchgrass grow up to 30 feet deep, and they constitute an enormous mass. Scientists have estimated that an acre of Switchgrass contains 4 tons of underground roots. As a result, Switchgrass is considered to have great potential for carbon sequestration. If you want your garden to contribute to mitigating climate change, plant some Switchgrass.
Here’s a close up. Switchgrass will tolerate a bit of shade, but prefers full sun. It can adapt to moist or moderately dry soils. While it gradually forms big clumps, it does not run or self-sow, at least not in our garden.
Switchgrass does a decent job of catching the light. It can be a tricky grass to photograph, though.
We have both the straight species Switchgrass and the popular cultivar ‘Shenandoah’, which grows to 3-4 feet. I just planted a couple more ‘Shenandoah’ in the Lamppost Bed and the Parkway Bed. They were wasting away at the local Home Depot, which had them on sale for almost nothing. They look happier now.
In addition to its compact size, ‘Shenandoah’ is popular for its red-tipped foliage. The whole plant is supposed to turn burgundy in fall, but that doesn’t happen with ours. The straight species does not tend to have much color, though it will turn the color of straw by early winter.
What are your favorite autumn grasses?
gardeninacity 
I have one big grass in my garden that I don’t know what it is. A friend gave it to me and said it was supposed to be part of her prairie planting but she didn’t care for it. It is sort of pretty but I am not a big fan of that type of grass. I have the Sea Oats too. It is a rascal for sure, popping up here and there and every where. I planted some Searsucker Sedge this fall. I love it. I have wanted some for a long time. I hope it takes.
Searsucker Sedge! What a great name! I have to go look it up now.
The seed heads of your sea oats really are beautiful, and I see why you can forgive them their waywardness. My favorite grass here is our native pink mthly grass. I just planted some in my garden and am looking forward to seeing their hazy pink plumes.
That is a beautiful grass, I don’t think it is hardy around here, though.
Oops that is pink muhly grass!
I love my grasses, but the sea oats are a nuisance. I also love looking at them over the winter but they are the dickens to cut down in the spring.
Very true. And yet they look so good.
The sea oats are beautiful, but I have been trying to get rid of them for years, without success. I don’t want them to escape into the neighborhood unintentionally. I think I started chamomile sprouting in the sidewalks in my neighborhood…. I do love ornamental grasses both tall and short, including switchgrass!
Once they are established I would imagine getting rid of them would be a struggle. I just try to keep them contained, and it’s not easy.
I have Northern sea oats too. They are so pretty, but I try to cut them back before they set seed. Also, have Shenandoah. Didn’t know if was helpful for climate change, so will embrace it even more!
Switchgrass: beautiful and with socially redeeming value.
Beautiful stuff! I like them both, but I don’t think I have enough sun for Switchgrass. My N. Sea Oats is starting to spread a little, but definitely not out of control yet. It’s really attractive, as you show here, when the seedheads start to color and with the sun backlighting them. 🙂
Switchgrass should have at least part sun, I think. Glad that your River Oats are restrained.
I have both River Oats and Switchgrass, growing next to each other. I plan to move the former and let them take over a bed away from other beds for the reason you cited – they pop up all over the place. The Big Blue Stem is doing well, the Little Blue Stem not so much. Then there is the Dwarf Fountain Grass, which is also trying to spread but not as much as River Oats, and a couple of problematic grasses that are non-native and supposedly invasive. Oh, and a clump of well-behaved pampas grass. Wow – I didn’t realize I had so many varieties! Fall is when they all shine.
Bluestems, both big and little, have done poorly for me.
I love your River Oats and Switchgrass growing together, and I’m ashamed to say although Australia has plenty of grasses, I don’t know the names of them, but I’m off to some gardens and parks to find out more about them.
I would be interested to know what ornamental grasses are native to Australia.
I fell in love with River Oats during one of the Flings but it’s propensity to pop up everywhere has dissuaded me from putting it in my garden. The switch grass, however, is on the list – do you know why your Shenandoah doesn’t turn colour in the fall?
I really don’t. Not enough sun, maybe?
Interesting info about Switchgrass roots. And a little intimidating.
I suppose so.
Both are lovely in their own opposite ways. No autumn grasses in my shady garden.
River Oats would probably grow in your shade.
Maybe someday I’ll give them a try.
Love those back-lit photos and agree that autumn beauty is amplified by grasses in the garden! C. latifolium enjoy a host of names; according to the Lady Bird Johnson Wildflower Center: ‘Inland Sea Oats, Indian Wood Oats, Wild Oats, River Oats, Flathead Oats, Upland Oats, Upland Sea Oats’!
That’s a lot of names. Maybe we should have a vote and pick just one.
I’ve grown Chasmanthium here but it doesn’t thrive unless it gets summer water, and I am notoriously stingy with that, every summer I try to see how little I can get away with. Panicum does really well in our summer drought, and I grow a lot of that, it’s my favorite grass. I also grow Calamagrostis ‘Karl Foerster’ and Stipa tenuissima, which do well too.
Those deep roots really help with the seasonal droughts.
I do like both of your grasses. I had no idea that switch grass roots ran so deep. Fascinating. I have a grass that seeds absolutely everywhere.xxx
I suppose there are a number that do that. They Wild Rye species around here are another one.
Switchgrass of some variety is native here but it only gets maybe 3 feet tall.
I like the way the river oats catch the sun.
Given all that water you get, wonder why they are so short.
You ask funny questions sometimes. I do not have a favorite autumn grass. I am not impressed by those that are trendy. I think that I would like yours just because they are something completely different.
Pampas grass is a serious problem here. There garden varieties of Cortaderia selloana that are not so invasive, but I do not trust them. Cortaderia jubata is the species that is such an invasive exotic specie.
Pampas grass is one that I don’t really like. Miscanthus in all its forms is another one.
Ha! So I am not the only one. I do not completely dislike the various miscanthus. I am just not overly impressed with it. It is such a fad that I sort of get tired of seeing it so commonly.
My Chasmanthium finally produced some beautiful seedheads this year after me being patient for about three years now…. I do buy small plants, but clearly it needed time to settle in! I love almost every grass I see these days. My favourite at the moment is Zebra Miscanthus, which is getting nicely established now.
I can’t get excited about Miscanthus. I like the Big and Little Bluestems but haven’t had much success with them.
I haven’t tried them but like the upright growth. Will have to give then some space one day and see how they do!
I love the sea oats, and Gulf muhly, and Indian grass, with its beautiful yellow heads. Still, the bluestems — little, big, silver, bushy — always make my heart go pitty-pat. Little bluestem especially will hold in dry arrangements beautifully. I have a vase filled with some I brought back from Kansas three years ago, and it’s still holding its seeds. I probably have more grasses in my apartment than some people have in their gardens.
We’ve used grasses in containers only as accents. The River Oats looks good in containers, but it will drop its seeds eventually.
Hello Jason, those are some lovely grasses. We don’t really have any in the garden mainly because we’re worried about how easily they can self-seed. I don’t suppose you know varieties or families of grasses that don’t and are much more well-behaved?
There are definitely a number of grasses that will not self-sow aggressively. Switchgrass is one of them. Bottlebrush Grass (Hystrix patula) is another. And the Bluestems don’t seed much.
What lovely grasses, they really enhance the garden, specially with the light shining on them. I love panicums, they are so light and airy.
Overall, my favorite grass.
Love your photos. Switch grass is a favorite of mine.
Same here!